Not applicable
This invention relates generally to heaters and, more particularly, to terminals for heaters used in semiconductor manufacturing.
One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to as chemical vapor deposition (CVD). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions can take place to produce the desired film. Plasma enhanced CVD processes promote the excitation and/or dissociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive species. The high reactivity of the released species reduces the energy required for a chemical reaction to take place, and thus lowers the required temperature for such CVD processes.
The substrate rests on a substrate support during processing in the chamber such as the formation of a layer on the substrate. The substrate support typically is a substrate heater which supports and heats the substrate during substrate processing. The substrate rests above the heater surface of the heater and heat is supplied to the bottom of the substrate. Some substrate heaters are resistively heated, for example, by electrical heating elements such as resistive coils disposed below the heater surface or embedded in a plate having the heater surface. The heat from the substrate heater is the primary source of energy in thermally driven processes such as thermal CVD for depositing layers including undoped silicate glass (USG), doped silicate glass (e.g., borophosphosilicate glass (BPSG)), and the like.
In a typical heater, a heating element such as a resistive coil is embedded in a heater body which may be made of a ceramic, a metal, or the like. To connect the heating element to a power source, heater terminals are provided between the interior and the exterior of the heater body. In a typical terminal, a plug is inserted into the heater body to connect to the heating element. A rod is connected to the plug from outside the heater body, typically by brazing, and is coupled with a power source. The electrical current flows from the power source through the heating element via the rod and plug connection. The rod and the plug are often made of different materials having different coefficients of thermal expansion. The differential thermal expansion and contraction of the rod and plug during brazing, for example, produces residual stresses in the heater terminal, which can lead to failure.
Embodiments of the present invention are directed to relieving the stresses caused by a mismatch in the coefficients of thermal expansion in the components forming the connections at the terminals of a heater. The connection is typically formed by inserting a rod which is connected to a power source into the cavity of a plug which is connected to the heating element in the heater body. The rod is typically connected to the plug by a brazed joint, and may further include a threaded connection. Stress relief slots are formed on the side wall of the plug around the cavity for receiving the rod. When the terminal is heated and then cooled during brazing, the slotted side wall of the plug can flex to avoid residual stress buildup in the braze material between the plug and the rod caused by differences in expansion and contraction between the plug and the rod.
In accordance with an aspect of the present invention, a heater comprises a heater body having an electrical heating element and a bottom surface, and a rod configured to be coupled with an electrical power source. A plug has a first end which is coupled to the heater body and extends into the heater body through the bottom surface of the heater body, and which is electrically connected with the electrical heating element. The plug has a second end which includes a cavity to receive a portion of the rod. The cavity is surrounded by a slotted side wall of the plug which is disposed outside of the heater body and includes a plurality of slots extending from the second end toward the bottom surface of the heater body and terminating near the bottom surface but before reaching the bottom surface. The slotted side wall is connected with the rod received into the cavity. The rod and the plug have different coefficients of thermal expansion.
In some embodiments, the slotted side wall of the plug has at least three slots extending from the second end toward the bottom surface. The slotted side wall of the plug may have four slots which are spaced about 90 degrees apart. The rod typically has a higher coefficient of thermal expansion than the plug. The portion of the rod received into the cavity of the plug is brazed to the slotted side wall of the plug with a braze material, or is threadingly coupled to the slotted side wall of the plug, or both.
In accordance with another aspect of the invention, a heater comprises a heater body having an electrical heating element and a bottom surface, and a rod configured to be coupled with an electrical power source. A plug has a first end which is coupled to the heater body and extends into the heater body through the bottom surface of the heater body, and which is electrically connected with the electrical heating element. The plug has a second end which includes a cavity to receive a portion of the rod. The cavity is surrounded by a slotted side wall of the plug which is disposed outside of the heater body and includes a plurality of slots extending from the second end toward the bottom surface of the heater body generally in an axial direction along an axis of the plug. The plug has an exposed length from the second end to the bottom surface of the heater surface. The slots are substantially longer than half the exposed length of the plug and terminating before reaching the bottom surface. The slotted side wall is connected with the rod received into the cavity. The rod and the plug have different coefficients of thermal expansion.
Another aspect of the present invention is directed to a method of forming a heater terminal for a heater which includes a heater body having an electrical heating element. The method comprises inserting a first end of a plug through a surface of the heater body into the heater body to electrically connect the plug with the electrical heating element. The plug has a second end which includes a cavity surrounded by a slotted side wall which is disposed outside of the heater body. The slotted side wall includes a plurality of slots extending from the second end toward the surface of the heater body generally in an axial direction along an axis of the plug. The plug has an exposed length from the second end to the bottom surface of the heater surface. The slots are substantially longer than half the exposed length of the plug and terminating before reaching the bottom surface. The method further comprises inserting a rod which is configured to be coupled with an electrical power source into the cavity at the second end of the plug and connecting the rod with the slotted side wall of the plug. The rod and the plug have different coefficients of thermal expansion.